A US Navy mini-submarine scanning the ocean bed has covered more than 80% of a 310 sq km (120 sq miles) search area in the southern Indian Ocean, without finding any sign of debris in water that is up to 4.5km deep.

Up to 10 military aircraft and 12 ships are currently taking part in the hunt. The daily operation, involving some two dozen nations, is already shaping up to be the most expensive in aviation history.

Australia said on Wednesday that it would not abandon the hunt, insisting that the cost of the operation was not a concern.

Prime Minister Tony Abbott said if the current underwater search was unsuccessful, a new strategy would begin.

Image copyrightReutersImage caption
The torpedo-shaped underwater vehicle - called a Bluefin-21 - has so far covered 80% of the target area

In a separate development, Malaysian Transport Minister Hishammuddin Hussein said that his country's cabinet had approved the formation of an international investigation team to "determine the actual cause of the accident so similar accidents could be avoided in the future".

Australia says that it is now consulting with Malaysia, China and the United States on the next phase of the search, which is likely to be announced next week.

Mr Abbott said a new search strategy would be put into action if nothing was found in the current seabed search.

"If at the end of that period we find nothing, we are not going to abandon the search, we may well rethink the search, but we will not rest until we have done everything we can to solve this mystery," he said.

"The only way we can get to the bottom of this is to keep searching the probable impact zone until we find something or until we have searched it as thoroughly as human ingenuity allows at this time," the Australian prime minister said.